The embassy's readings, published on Twitter, often clash with official data. On Sunday, it rated Beijing's air as "hazardous" as thick smog blanketed the city, while official Chinese measurements said the pollution was "slight."

"I'm not clear about their way and methods of monitoring or how they ensure the accuracy," said Du Shaozhong, spokesman for the Beijing Municipal Environmental Protection Bureau, according to the Beijing Times.

"But I feel their way of releasing (the data) is more like hype, and not a very serious attitude toward research." The bureau was not immediately available for comment when contacted by AFP.

According to state media reports, the discrepancy between the readings stems from the fact that China measures large polluting particles, while the US focuses on smaller particles deemed more dangerous to human health. As such, a growing number of local residents are turning to the American figures rather than the official ones, and authorities have pledged recently to improve the way they measure air quality. In a separate report on Friday in the Beijing Morning Post newspaper, Du said the city was capable of monitoring smaller particles but no timetable had yet been set for the release of these figures.

International organisations including the United Nations list Beijing as one of the most polluted cities in the world, mainly due to its growing energy consumption -- much of which is still fuelled by coal. The discrepancy between the two sets of data has sparked a debate in Chinese media and on the web.

"Figures by some local governments show the air pollution index is dropping in some cities, such as Beijing," the state-run Global Times said in an editorial on Monday. "But some Beijing citizens complain the figures do not match their experience."